I bought a version 1 Eclipse off ebay a few months ago, and was successful in upgrading to version 4.
I followed these instructions from an Eventide staff member:
thing you will need to do is create a user account on our website. After that
you will need to register your Eclipse. After registering it, you will be able
to access the software upgrades on our website. They will be listed under the
Support page for the Eclipse. You will need to carefully read the release notes
for both of the following versions. Since you have an older version you will
need to upgrade to V3.51 first and then to V4.01. All of this can be done with
a compact flash card and a compact flash card reader connected to your
computer. Be aware, that the compact flash card must be formatted as FAT and
not FAT32. Many of the newer, larger cards are FAT32 and will thus need to be
formatted as FAT for this to work. This formatting procedure can only be done
in a PC, not a Mac. The rest of the process can be done in a Mac. You may also
need to do the Bootloader update that is mentioned on that page. The rest of
the instructions are in the release notes.
The Eclipse I purchase would not hold settings after power down, and it turned out I needed to replace the internal battery, which was easy to do and cost about $5.
I really like my Eclipse, and prefer it to the 3500.